Optimizing exercise range of motion to maximize muscle growth is a popular topic to discuss. As new research emerges, it often leaves you with more questions about the fundamental mechanisms and application of hypertrophy training. Mechanical tension is known as a primary driver of hypertrophy. Therefore it stands to reason that training a muscle through larger ranges of motion will create more tension, resulting in a greater hypertrophic stimulus. Although this makes sense at face value, it’s ultimately an unsatisfactory answer. At deeper levels of analysis, mechanical tension alone (or at least our current model) can not explain some of the observed outcomes we see both in the literature and anecdotally. The aim of this article is to provide a brief review of the topic, provide context to the ROM discussion, and offer practical recommendations to implement into your own training.
A recent meta-analysis aimed to compare partial to full range of motion on various outcomes including strength, hypertrophy sport performance, body composition, and power (1). Researchers found “our results suggest that using a full or long ROM may enhance results for most outcomes (strength, speed, power, muscle size, and body composition)”. However, the magnitude of these differences are often small to trivial and do not clearly explain the benefit of training through longer ranges of motion. For example, you can have subjects train partials but split the group into those training partials in the lengthened muscle position vs those training partials in the shortened muscle position. What you’ll find is the group training partials through the lengthened position will see greater hypertrophy when all other variables are equated.
A 2021 paper by Maeo et al. compared the effect of seated vs prone hamstring curls on hypertrophy outcomes. Researchers found “Training-induced increases in muscle volume were greater in Seated-Leg versus Prone-Leg for the whole hamstrings (+14% vs +9%) and each biarticular (+8%–24% vs +4%–19%), but not monoarticular (+10% vs +9%), hamstring muscle” (2). You’ll notice the seated leg curl leads to greater hypertrophy in the biarticular (a muscle that crosses two joints) but not the monoarticular (a muscle that crosses only one joint) muscles. This is because biarticular muscles cross the hip and the knee, and the seated position puts them under greater stretch. So although the exercise range of motion is standardized, the outcomes biased the seated (lengthened position) position.
The resistance profile is also important to consider since the loading of an exercise may change to varying degrees during the active range of the movement. For instance, the loading of a DB vs cable when doing lateral raises changes significantly. Peak torque changes depending on the loading. In the image below you can see when peak torque is reached during each exercise.
We’ve already established that loading the lengthened vs shortened position can alter the magnitude of hypertrophy stimulus. Therefore, even if the active ROM and body positions are identical, the resistance profile can independently alter the raw stimulus magnitude. So what does this mean for you? In most instances it’s best to use a combination of ranges that trains the muscle in both the shortened and lengthened position. Researchers have also observed that training muscles in the lengthened position specifically leads to greater distal hypertrophy. For the purposes of bodybuilding where the development of specific symmetrical development is important this can mean altering exercise selection, loading, and execution to bias various ranges based on the needs of the lifter. It’s important to note that the exercise range of motion may not always align with the functional action of the muscle being trained. Thus, a shorter exercise range of motion may still train the full functional range of motion of the muscle. A great example of this is a chest supported row. If you want to target the lats your range will be shorter than if your objective was to target the upper back. As you contract the lats eventually you’ll reach a functional end range so to speak where going further would shift more loading demands onto the upper back musculature as you retract your scapulae together (it’s more complex than just that but you get the point). To clarify, I’m not saying this is bad just giving an example of how exercise range of motion and active range of muscle function may differ.